Conventional laundry dryers include a rotatable drum in which fabrics are tumbled during the drying process. Some dryers include the capability to introduce steam into the drum to reduce wrinkles in the fabrics. However, these prior art systems are unable to optimally retain steam in the drum while maintaining optimal drum rotation, which reduces the steam's usefulness. Such laundry dryers include condenser clothes dryers and vented clothes dryers.
Condenser clothes dryers circulate air exhausted from the drum through a heat exchanger/condenser to cool the air and condense its moisture. They subsequently recirculate it back through the drum. The recirculated air retains a portion of its moisture when reintroduced into the drum after traveling through the condenser. The level of moisture content can be increased via the addition of atomized water to the recirculated air prior to reintroducing it to the drum. See, e.g., U.S. Pat. No. 7,162,812.
Vented clothes dryers draw air from the surrounding area, heat it, blow it into the drum during operation, and then exhaust it through a vent to the outside. Some vented dryers introduce steam into the drum for reducing wrinkles in the clothes, but are unable to retain steam in the drum for optimal de-wrinkling or refreshing benefits. Further, some vented dryers introduce steam into the drum while intermittently rotating the drum, which may provide sub-optimal tumbling during steam exposure and can limit steam dispersion into the clothes.
Some vented dryers have separate motors for rotating the drum and for driving the air circulation blower. This permits the drum rotation speed to be set independently of the blower, but these systems suffer drawbacks related to the use of two motors instead of a single motor, such as increased costs and control complexities. Conventional single motor systems typically have fixed speed on-off operation. A motor provided with a variable speed control would present the opportunity to periodically slow the blower speed along with the drum rotation speed, or the motor could be turned off for short periods to stop the blower while the drum rotates via its momentum. See, e.g., U.S. Pat. No. 7,325,330. However, these systems may provide sub-optimal tumbling during steam exposure due to intermittent or slower drum rotation speeds, which can limit steam dispersion into the clothes. In addition, variable speed motor control adds complexity and cost.
Reversing dryers, i.e., dryers that reverse the rotation direction of the drum, are also known. In some instances, such reversal has been provided with a single motor that drives both the blower and the drum, and with the blower creating a lower airflow rate when driven in the reverse direction. See, e.g., Joslin U.S. Pat. No. 5,555,645 and Hughes U.S. Pat. No. 2,961,776.